This invention relates to shutter mechanisms and, in particular, electromagnetically driven shutter mechanisms.
A wide variety of shutter mechanisms have been used in cameras. These tend to be mechanically sophisticated in construction as well as operation. Typically, shutter blades are rotated, pivoted or generally linearly reciprocated with respect to each other for controlling the passage of light along an optical path. U.S. Pat. Nos. 3,781,099; 3,782,255; and 3,942,183 are illustrative of different kinds of shutter blades. Usually, these mechanisms include a stored energy device, such as a mechanically tensioned spring, for driving the shutter blades to an open condition. These systems function satisfactorily and provide commercially acceptable reliability. Because of their relative intricacy in construction and operation, however, they have certain limitations. For instance, use of tensioned spring mechanisms gives relatively fixed characteristics (not programmable). Moreover, they tend to be relatively large, bulky and susceptible to failure. Because they are mechanically driven, their dynamic performance is not as accurate or reliable as it could be.
Various proposals have been made for improving upon such shutter mechanisms. Moreover, with the advent of miniature cameras, there has also been developed a need for miniature shutter mechanisms. Obviously, the use of relatively large springs for driving the shutter blades in miniature cameras is unsuitable.
Some proposals have suggested replacing the spring tensioning mechanism with an electromagnetic actuator. In this regard, U.S. Pat. No. 4,024,552 even discloses shutter blades which actually form part of the electromagnetic actuator. However, this actuator nevertheless uses springs for returning the blades to their blocking condition. In fact, a number of shutter mechanisms using an electromagnetic actuator for driving the shutter blades to an unblocking condition rely upon springs for returning the blades to their blocking condition. Thus, springs are still required.
Besides, conventional electromagnetic actuators, in general, employ annular field coils with magnets moving into and out of their core. These are considered bulky. Hence, the overall configuration of the shutter mechanism is bulky and less than ideal for miniaturization. Moreover, use of annular field coils in these actuators is not highly efficient.
There have been proposals for springless shutter mechanisms. One such proposal is described in commonly-assigned U.S. Pat. No. 3,882,552. This patent discloses use of a rotary stepper motor for driving the shutter blades between open and closed orientations. A shortcoming is that the rotary stepper motor is somewhat bulky. Another proposal for a springless shutter mechanism is described in commonly-assigned U.S. Pat. No. 4,265,530, issued to the inventor of the instant application. The system described uses not only a linear motor, but an electromagnetic clutching mechanism for driving the shutter blades between unblocking and blocking conditions.
Another proposal for a springless shutter is disclosed generally in U.S. Pat. No. 4,121,235. In this patent, there is disclosed an electromagnetic shutter mechanism employing a pair of solenoids having annular field coils which actuate a pair of shutter blades interconnected through a force transmitting lever. There are a number of drawbacks associated with this approach. For instance, such an actuator uses bulky and relatively inefficient solenoids.